The successful electrochemical synthesis of 1,4-butanediol from 2-bromoethanol is demonstrated by U.S. Pat. No. 4,253,921 to Baldwin et al; however, the process therein disclosed produced routine yields of only about 20 percent using the most favorable conditions set forth in that specification.
Product yield in a process of this type is defined as the ratio of the amount of product actually produced to the amount of product that would theoretically have been produced if all of the principal reactant provided and been converted to the desired product. Factors that tend to reduce the yield or lead to inefficiencies in the electrochemical process are side reactions and undesired transitions of intermediately formed radicals and compounds. As an example, in the case of the electrochemical synthesis of 1,4-butanediol, ethylene has been observed evolving from the cathode region of the cell. This may arise from an intermediate radical produced by the electrochemistry of the process being converted. The undesired conversion may be suppressed to some extent by the adjustment of the catholyte pH to not substantially below 7, preferably within the range of 8 to 9 as disclosed in the Baldwin patent. However, even under these favorable conditions yields still remain in the 20 percent range.
It will be understood that the term anolyte refers to the solution contained in the anode compartment of an electrochemical cell, while catholyte refers to the solution retained in the cathode compartment of such a cell.
The use of an organic group substituted for the hydroxyl hydrogen, specifically the acetate of 2-bromoethanol, during the electrochemical synthesis process is disclosed in Cipris (Journal of Applied Electrochemistry, 8, 537-544 and 545-547, 1978). This synthesis involved the use of dimethylformamide as the primary solvent present in the electrolytic cell and utilizes only trace amounts of water. It would be more desirable from a commercial production point of view if an aqueous based solvent could be utilized. The ester derivatives would not be suitably stable in an aqueous environment, particularly at the high pH values cited in U.S. Pat. No. 4,253,921 to Baldwin et al., since such derivatives would be extensively hydrolysed under those conditions.
Therefore, there is a need to improve the yields of the electrochemical type coupling process leading to the production of 1,4-butanediol and other symmetrical alkanediols in order to make the process commercially attractive.
Since it is believed that an aqueous based electrochemical system will have considerably greater industrial potential than a system utilizing no water or only trace amount thereof, the work on improving the yields of the product 1,4-butanediol concentrated on utilizing an electrochemical cell environment corresponding to the most successful system identified in U.S. Pat. No. 4,253,921 to Baldwin et al.